Rigidity and Strength of Orthotropic Reinforced Concrete Waffle Slabs

Abstract

This paper presents the results of an experimental study of reinforced concrete waffle slabs with a square layout of ribs. Tests to failure were carried out on eight large-scale (1/4-in. scale) models with varied rib spacing and rib depth. The validity of the “equivalent thickness” concept was also examined by testing two related slabs. The results for the rigidities in the elastic-uncracked and elastic-cracked ranges were compared with predicted values obtained from three different methods. The theoretical analysis based on the conventional orthotropic plate theory gave satisfactory predictions but involves an elaborate procedure for determining the torsional rigidities. The equivalent thickness approach, which was modified to apply to the cracked as well as the uncracked ranges, gave moderately higher values for the rigidity than test results. An alternative simplified approximate method based on the “effective modulus of elasticity” is also proposed. Predictions for the rigidities by the proposed method were on the safe side and reasonably close to test results.